Early gene therapy trials for haemophilia B show promise

Preliminary results from a trial of viral-based gene therapy for haemophiliahave shown that four of the six patients treated were able to stop taking clotting treatments.

Haemophilia Bis a rare disease where inherited mutations prevent the production of a crucial component of the blood clotting cascade, factor IX. The only treatment is frequent injections of synthetic factor IX, which is very expensive.

The adeno-associated virus (AAV) based gene therapy vector was used to deliver normal copies of the factor IX gene to the liver cells of patients at different levels. Factor IX production was increased in all patients to between 2 and 12% of normal levels.

Dr Amit Nathwani from University College London commented: "This is the first study that has shown that you can actually achieve stable, long-term, therapeutic level of expression [factor IX production] in subjects with severe haemophilia B, so it's a fantastic start”.

Researchers hope that if the treatment proves safe and effective in longer-term trials, it may allow haemophilia B sufferers to lead more normal lives, managing without factor IX injections except in cases of injury. A similar gene therapy approach is also under investigation for the more common form, haemophilia A, which affects around five times as many people.

Comment: The main problem with gene therapy is to achieve long-term expression of the healthy genes; however, to people used to receiving injections perhaps several times weekly, having ‘booster’ treatments to maintain gene expression might be acceptable, and even cost-effective. The safety of repeat administration would be another concern, of course.